The present invention relates generally to roller apparatus such as, for example, back-up rollers used to support work rolls.
Work rolls are used in tandem sets to shape metal through compressive forces. The supporting back-up rollers tend to have a relatively larger diameter than the work rolls. Back-up rollers must be capable of applying very high forces, as much as 300,000 pounds of force.
Conventional back-up rollers comprise a bearing in which the axle is received in the inner race and the outer race is received in the roller. Bearing elements such as ball or cylindrical members are rotatably received between the races so that the roller is rotatable relative to the axle. Since there are size constraints on the rollers, the wall thickness of each of the inner and outer races for back-up roller bearings is conventionally limited to typically no more than about xc2xd inch. Bearings, for example, for cam followers and bearing wheels, have been provided wherein the wall thicknesses of the inner and outer races have been in excess of 1 inch. The rigidity of a race is related to its effective wall thickness (which includes the thickness of an axle or roller to which it is rigidly mounted), and the bearing capacity is a function of the rigidity of the races. Thus, the capacity of such conventional back-up rollers is limited by the rigidity of the least rigid of the races.
Back-up bearings have been provided wherein the inner race is mounted over an axle and has a variable thickness ranging between about xc2xe inch and about 1{fraction (1/16)} inch and wherein the outer race serves as the roller and has a variable thickness in excess of about 3 inches and the surface of which has a shore hardness of 78 to 83.
One type of back-up roller heretofore provided by Applicant to a customer comprises two spherical roller bearings with an inner race fitted to an axle and an outer race fitted to an outer shell or roller composed of AISI 4140 heat-treated steel having a Rockwell C hardness of 45. Both the bearing life and the shell life were however considered unacceptable. In order to improve the shell life and also hopefully the bearing life, the customer requested that the shell be made instead of cast 420 stainless steel having a Rockwell C hardness of 50. While this did improve the shell life, the bearing life nevertheless remained unacceptable to the customer.
Back-up rollers are placed at spaced positions both circumferentially about (from overhead and from the floor) and axially along the work rolls. Each back-up roller must be accurately positioned, both top to bottom and left to right, and custom precision grinding is required to achieve the necessary accuracy during every changeover.
As the back-up rollers wear and their outer diameters accordingly decrease, they do not bear as hard against the work rolls with the result that the work rolls are undesirably more prone to deflect. When this occurs, it has been necessary with conventional back-up rollers to replace a worn roller with a new one. It is, however, considered desirable to increase the useful life of the back-up rollers so that they may need replacement less often.
In order to extend the useful life of such a back-up roller, in accordance with the invention disclosed and claimed in the parent application, the height (distance from the back-up roller axle to the back-up roller circumference or radially outer surface) thereof was adjustable by rotating an eccentric mount through which the axle is disposed and thereby translating the roller in a radial direction thereof. In order to rotate the eccentric bushing, a pair of circumferential slots were provided in the eccentric bushing, and force was applied to the eccentric bushing at ends respectively of the slots to push the eccentric bushing in opposite circumferential directions respectively.
FIGS. 1 to 3 illustrate generally at 10 an assembly of a pair of back-up rollers 12 which are used to support work rolls in accordance with the invention disclosed and claimed in the parent application. It should be understood that an assembly may include only one, three, or any other number of rollers 12. Work rolls 15 are rolls which perform work on material which is passed between the work rolls, for example, flattening a sheet of metal. In order to perform the work, suitable force must be applied to the material, and back-up rollers 12 apply force to the work rolls 15 to aid them in performing the work.
The assembly 10 includes a housing 14 comprising a generally rectangular base plate 16 to opposite sides of which are attached, such as by welding or other suitable means, a pair of side plates 18 each having a pair of semi-circular openings or arches, illustrated at 20, in its upper edge for the mounting of the rollers 12 respectively. Illustrated at 29 are a plurality (the assembly is shown to have three) of beams at the ends and center of the side plates 18 respectively and about midway of the height thereof, each beam 29 extending between and suitably attached to the side plates 18 such as, for example, by welding for bracing the housing 14. A pair of cap plates 22 are attached to the upper edge of each of the side plates 18 each by means of a pair of fasteners 24 the shanks of which are received in apertures 23 in the respective cap plate 22 and which threadedly engage threaded apertures 27 in the respective side plate 18 or by other suitable means. The fasteners 24 may, for example, be socket head cap screws the heads of which are received in counterbores in the cap plates 22. Slotted (for receiving a screwdriver) plugs 25 are screwed into the upper portions of the bores to cover and protect the bolts 24. The bottoms of the threaded apertures 27 are suitably vented, and the vent holes (not shown) are closed by vent plugs 31. Each cap plate 22 has a semicircular opening or arch, illustrated at 26, in its lower edge which is complementary to the opening 20 in the respective side plate 18 to provide a circular passage, illustrated at 28, wherein the pair of passages 28 on one side of the housing are in alignment with the pair of passages 28 on the other side of the housing.
A bushing 30 is received in each of the passages 28 to rotatably (frictionally) engage the respective side plate 18 and cap plate 22 and extends axially inwardly a small distance beyond the inner side surfaces thereof. The axially inner corners of the cap and side plates 22 and 18 respectively are suitably chamfered, such as at an angle of about 45 degrees, as illustrated at 32 and 34 respectively. The bushing 30 has a circumferential ridge 33 extending from its radially outer surface which frictionally engages complementary notches 36 and 38 in the chamfered corners 32 and 34 respectively to locate the position axially of the bushing 30 and prevent its movement axially out of the assembly 10.
An axle 40 is received within each respective pair of bushings 30 and is attached thereto to prevent relative rotation therebetween by a dowel 74. By xe2x80x9cdowelxe2x80x9d is meant to include other suitable attachment devices such as a pin or key. The dowel 74 is received in a bore, illustrated at 75, which extends diametrically across the axle 40 in each end portion thereof and in bores, illustrated at 77, in the respective bushing 40.
Rotatably positioned about the axially central portion of the radially outer surface of the axle 40 are a plurality of circumferential rings or groups of roller bearing elements 42, preferably cylindrical. For example, there may be 8 side-by-side groups each having 22 roller bearing elements positioned circumferentially about the axle 40. A thin flat washer-shaped spacer member, illustrated at 44, is positioned between each group and the adjacent group of roller bearing elements 42. The radially inner axle-engaging edge of each spacer member 44 is scalloped such as by a plurality of half-moon cutouts, similarly as illustrated at 145 in FIG. 6, spaced circumferentially about the inner edge or by other suitably shaped cutouts to allow grease passage along the length of the axle.
Encircling all of the roller bearing elements 42 is a bushing or sleeve 46. For the purposes of this specification and the claims, the sleeve 46 is part of the roller 12. Thus, the roller 12 is considered to be a laminated or two-piece roller comprising the outer member 11 (which may also be referred to herein as the roller) and the sleeve 46. The sleeve is received within the bore 48 of the roller outer member 11. As discussed with reference to FIGS. 4 to 6, the roller 12 may alternatively be of a single piece construction or may otherwise be suitably constructed.
Each end of the bore 48 has an increased diameter to define a cutout, illustrated at 50, in the radially inner and axially outer surfaces of the roller outer member. An end plate 52 is received circumferentially about the axle 40 between each bushing 30 and the roller bearing elements 42 and respective sleeve 46 and is press-fit or frictionally received in the respective cutout 50 to thereby fix the position axially of the roller 12 and rotates with the roller 12. A groove is provided in the radially inner surface of each end plate 52 to receive grease to seal the radially inner surface thereof. While not shown in FIGS. 1 to 3, the groove is similar to the groove illustrated at 153 in FIG. 5. A suitable seal 84, such as an axial lip seal, is provided to extend circumferentially about each bushing 30 on the axially inner end portion thereof and with a lip 86 which engages the respective end plate 52. In addition to supporting the rolling elements 42 from skewing and coming out, the end plates 52 are provided to increase roller rigidity and thus roller stability, provide hardened surfaces to receive thrust, and to provide a hardened smooth finish for the seal 84 to rub against and thereby have longer seal life.
At 54 are bores, for example, 4 bores circumferentially spaced in each of the end walls of the axle 40 for receiving a spanner wrench for purposes of assembly. At 56 is a hole for use in driving the axle for grinding.
For each roller 12, a grease passage or bore, illustrated at 58, extends from an opening in the lower outer surface of the base plate 16 through the base plate height then partially through the height of a side plate 18 to a point of termination or blind end. A pipe plug 60 closes each grease passage opening. Access to the forward grease passage is through the opening. Since the grease passage opening for the rear roller assembly may be inaccessible, a grease passage, illustrated at 76, extends horizontally over a portion of the base plate length and connects with the passage 58 for the rear roller assembly for supply of grease thereto. The passage 76 is closable at one end in an end wall of the base plate 16, which may be a more accessible location, by a pipe plug 78 and extends beyond the corresponding grease passage 58 to a tapped hole 80 used to receive a hold-down fastener (not shown) for connecting the assembly to a base, the passage 76 providing a vent as well as a means of lubricating the hold-down fastener.
Another grease passage, illustrated at 62, receives grease from passage 58 adjacent the blind end and extends therefrom toward the axis, illustrated at 64, of the axle 40 and to an outlet from the side plate 18. An adjoining grease passage, illustrated at 66, receives grease from passage 62 and extends radially through the bushing 30 to an outlet in the radially inner surface thereof. An adjoining grease passage, illustrated at 68, in the axle 40 receives grease therefrom and delivers it to a radially central passage, illustrated at 70, of the axle 40. The grease is delivered for lubricating the roller bearing elements 42 via a passage, illustrated at 72, which extends radially outwardly in opposite directions from an axially central point of passage 70. A threaded portion, illustrated at 82, of the passage 70 adjacent each dowel 74 receives a suitable pipe plug (not shown) to close the radially central grease passage 70.
As previously discussed, the use of a conventional bearing having inner and outer races and rolling elements therebetween interposed between the axle and roller would be limited in race thickness, the typical race thickness being about xc2xd inch. Therefore, the races conventionally used are eliminated so that the rolling bearing elements 42 are disposed between the axle 40 and roller 12 which accordingly function as an inner race and an outer race respectively. This allows increased wall thickness to the xe2x80x9cbearing racesxe2x80x9d for increased rigidity and accordingly increased bearing capacity. Thus, the roller wall radial thickness, illustrated at 149 for the back-up roller shown in FIG. 5, may be, for example, about 1xc2xd inch, and the axle wall radial thickness, illustrated at 155 for the back-up roller shown in FIG. 5, may be, for example, about 1xc2xd inch to thereby provide what is considered to be about double the capacity than would normally be provided if conventional bearings having thinner races were used. The terms xe2x80x9cradialxe2x80x9d and xe2x80x9cradiallyxe2x80x9d are defined, for the purposes of this specification and the claims, unless otherwise specified, as a direction toward or away from the axis 64 of axle 40, and the terms xe2x80x9caxialxe2x80x9d and xe2x80x9caxiallyxe2x80x9d are meant to refer to direction parallel to the axis 64. The thickness 155 would be equal to the radius of a section of the axle 40 taken in a radial plane if the axle does not contain a central passage such as lubrication passage 70 therein. The thickness 149 is meant to include the total thickness of parts of a laminated roller such as parts 11 and 46 of the roller of FIGS. 1 to 3. Preferably, the thicknesses 149 and 155 are each at least about 1 inch in order to provide adequate bearing capacity.
In order to extend the back-up roller life, the bushing 30 is eccentric. Thus, when the back-up roller is worn as well as during installation, the bushing is rotated to translate the roller 12 radially to a position where it is closer to the respective work roll and in a desirable position, as when unworn, to bear against the respective work roll with sufficient force so that deflection of the work roll does not occur. In accordance with FIGS. 1 to 3, the bushing 30 is shown to be rotatable by means of a pair of circumferential slots, illustrated at 88, therein extending in opposite circumferential directions to blind or closed ends, illustrated at 90. Set screws 92 (only one shown), which may, for example, be half dog set screws, are threadedly receivable in threaded apertures, illustrated at 94, in the housing cap plate 22. These apertures 94 extend in directions circumferentially and radially inwardly of the eccentric bushing 30 toward the blind ends 90. A ball element 96 is provided in each aperture 94 ahead of the set screw 92 to afford point contact with the bushing 30 to prevent binding. The set screws 92 thus bear against the ball elements 96 which in turn bear against the blind ends to push the eccentric bushing 30 circumferentially. By pushing on the bushing 30 at the blind ends 90 by means of the set screws 92 and ball elements 96, the bushing 30 is rotatable through a small angular distance.
In addition to effecting eccentric bushing placement so that it stayed tight and did not damage the housing and then to confirm that it would remain tight over a long period of time (years), a major problem has been insufficiency of the amount of height adjustment. It is also important that, after any height adjustment, all of the roller elements share the load. Modifications made to the roller of FIGS. 1 to 3 for the purpose of solving, inter alia, these problems are discussed hereinafter.
As initially installed, the roller height was adjustable through about 0.008 inch. It was discovered that the end plates (which enclose the rolling elements at the ends and which are fitted in cutouts in the roller) were cracking. This was corrected by increasing the radiuses of end plate corners and corresponding cutout corners from about {fraction (1/32)} inch to about {fraction (3/32)} inch and by press fitting (instead of slip-fitting) the end plates into position in order to reduce distortion and flexing of the roller. A bevel was also added to the roller to reduce stresses in the roller corners.
In order to improve the bearing life, the back-up rollers were made with the inner race serving as the axle and the outer race serving as the roller, and the outer race was made of a two-piece or laminated construction comprising an outer member of cast 420 stainless steel having a Rockwell C hardness of 50 (so as to not mark the work rolls) and a harder inner sleeve of AISI 52100 bearing steel having a Rockwell C hardness of 60. When test results showed that, although the back-up roller assembly life had been improved, the outer members were wearing and in some cases fatiguing (cracks in corners of end plates) too rapidly, they were improved by making the roller as a single piece of D2 tool steel having a Rockwell C hardness of 60 (option 1) for higher wear resistance as well as strength and hardness. Additional test results in the year 2000 indicated that, because of the increased hardness of the D2 tool steel material, the life of the work rolls was reduced. It is now believed that by constructing the roller inner sleeve of AISI 52100 bearing steel having a Rockwell C hardness of 62 and the roller outer member of forged 420 stainless steel having a Rockwell C hardness of 52 (option 2), ideal wear of both the outer and inner members of the roller as well as the work roll should now be achieved. It was also discovered that some applications are of such a severe nature that the benefit of the robust construction of the solid D2 roller (option 1) would outweigh the reduced life (increased wear) of the work roll, and, accordingly, it has been decided to offer both options 1 and 2 to customers.
It was also discovered that the rolling or bearing element spacers were too tight against the axle and not adequately sharing the load and that the grease was not flowing well from the middle to the outside rolling elements. This was remedied by scalloping (making semi-circular cutouts) the circular edges defining the inner diameters of the spacers and by increasing the spacer outer diameter to give back surface area lost due to the scalloping. The flatness of the spacers was increased to reduce the amount of acceptable wavyness (for tighter tolerance).
It was further found that the eccentric bushing was not staying tight enough within its housing, and this was remedied by making the housing cap out of armor plate (1xc2xd inch thick) instead of standard carbon steel.
It was also found that the amount of eccentric adjustment was insufficient especially in view of the need to adjust for inaccuracies in set-up. The angle, illustrated at 21 in FIG. 1, of the pair of slots 88 used for adjustment of the eccentric bushing was increased from 46 to 73 degrees to obtain the necessary amount of roller adjustment. When it was found that this did not achieve the desired amount of roller adjustment since adjusting set screws 92 were oriented generally at tangents to the slots respectively, the angle 21 was reduced to about 50.54 degrees.
An improvement made in the year 2000 is the provision of an increased length to a closed-off grease slot to 1xe2x85x9c inch so as to open it up.
The achievable amount of roller translation or height adjustment of the eccentric bushing, which is desirably about plus or minus 0.018 inch or more (at least about 0.015 inch), was still unduly limited, i.e., only about plus or minus 0.012 inch. Thus, there was some cause other than slot length for the limited height adjustment.
Moreover, the eccentric bushings at opposite ends of the roller may not adequately share the load if the housing dimensions at the opposite ends are off by as much as perhaps 0.001 inch, i.e., while one side of the roller may hit or engage the work roll, there may still be a gap between the roller and work roll on the other side with the result that the one side may undesirably bear all of the load.
It is accordingly an object of an aspect of the present invention to achieve adequate height adjustment for the back-up roller.
It is another object of the present invention to compensate for such small inaccuracies in the housing or otherwise so as to cause both bushings to share the load equally.
In order to achieve adequate height adjustment for the back-up roller, in accordance with the present invention, a portion of the eccentric bushing between the slots 88, which was found to be interfering with the movement of the adjustment set screws into the slots, was removed by extending the slots to each other thus making the pair of slots 88 into one single slot.
In order to compensate for small inaccuracies in the housing or otherwise so as to cause both bushings to share the load equally, each eccentric bushing has holes in which the dowel is received which are oblong so as to have a greater length circumferentially of the bushing than the diameter of the dowel 174 so as to allow some circumferential movement of each eccentric bushing independently of the other bushing.
The above and other objects, features, and advantages of the present invention will be apparent in the following detailed description of the preferred embodiments thereof when read in conjunction with the accompanying drawings wherein the same reference numerals denote the same or similar parts throughout the several views.